Valve confirms next-gen Source engine exists and is just 'waiting for a game to roll it out with'

Valve confirms next-gen Source engine exists and is just 'waiting for a game to roll it out with':
Valve boss Gabe Newell has been caught on camera (lots of cameras, actually), explaining that Source 2 is real and is in development. It's just waiting for a game to release with. Now what could that game be...?
 Source:Google Reader